When unmanned flying vehicles were first introduced to the U.S. military, the ability to control them from afar wasn't very sophisticated. So the first drones flew along pre-set paths, operating off an internal navigation system. This led to servicemen informally referring to any machine that flew without human control a "drone," and Germany still has some like this in service today. That said, the "not being controlled by a human" part of the definition has since been lost to everyday use.